The proposed study consists of 2 parts. The first of these will involve a study of the mechanisms by which coproantibody prevents the adsorption of vibrios to the intestinal mucosa, and by which adsorbed vibrios are inhibited in their growth or killed in the presence of coproantibody. These phenomena have recently been described by us. Attempts will be made to identify the cell surface components involved by inhibition studies with various fractions of material isolated from mucosal and bacterial cells. Similarly, the fragments of the immunoglobulin molecule involved will be determined. The second part of the proposed study will be an investigation of the effect of normal flora on host defense mechanisms against experimental cholera. The mechanisms to be studied include (a) the degree of adsorption of vibrios to the mucosal surface, (b) toxin production in the intestinal tract, (c) intestinal motility and (d) growth rate of vibrios in the intestinal tract. Various types of intestinal flora will be established in germfree mice. After an interval of time, the "normal" flora will be eliminated with antibiotics, and the mice challenged with antibiotic resistant vibrios. This allows testing for the above parameters in the absence of direct antagonism (or "bacterial interference") on the part of the "normal" flora. The different types of "normal" flora to be used will include the fastidious anaerobes which are predominant in the large intestine of normal mice, and which can now be cultured with ease by means of a recently developed anaerobic glove box technic.